1. Field of the Invention
The present invention relates to anti-counterfeiting devices. Specifically, it relates to security threads used in banknotes and other documents for authentication purposes.
2. Brief Description of the Related Art
Security threads are security elements very often used in banknotes to help make counterfeiting more difficult and to serve for authentication.
Numerous threads have been described, designed both to propose securities which are difficult to reproduce and also to produce an attractive visual appearance.
EP 1 819 525 B1 discloses a security element comprising flake pigments, which can be oriented under the effect of a magnetic field thereby making it possible to observe an underlying print, for a direction of observation substantially parallel to the orientation of the pigments. The security element has two zones in which the pigments are oriented differently so as to observe an appearance/disappearance of the underlying patterns when the direction of observation changes. The security element may be in the form of a thread.